diff --git a/day9/backup.sql b/day9/backup.sql
new file mode 100644
index 0000000..9f33021
--- /dev/null
+++ b/day9/backup.sql
@@ -0,0 +1,171 @@
+-- MySQL dump 10.13  Distrib 5.7.33, for Linux (x86_64)
+--
+-- Host: localhost    Database: studb
+-- ------------------------------------------------------
+-- Server version	5.7.33-0ubuntu0.16.04.1
+
+/*!40101 SET @OLD_CHARACTER_SET_CLIENT=@@CHARACTER_SET_CLIENT */;
+/*!40101 SET @OLD_CHARACTER_SET_RESULTS=@@CHARACTER_SET_RESULTS */;
+/*!40101 SET @OLD_COLLATION_CONNECTION=@@COLLATION_CONNECTION */;
+/*!40101 SET NAMES utf8 */;
+/*!40103 SET @OLD_TIME_ZONE=@@TIME_ZONE */;
+/*!40103 SET TIME_ZONE='+00:00' */;
+/*!40014 SET @OLD_UNIQUE_CHECKS=@@UNIQUE_CHECKS, UNIQUE_CHECKS=0 */;
+/*!40014 SET @OLD_FOREIGN_KEY_CHECKS=@@FOREIGN_KEY_CHECKS, FOREIGN_KEY_CHECKS=0 */;
+/*!40101 SET @OLD_SQL_MODE=@@SQL_MODE, SQL_MODE='NO_AUTO_VALUE_ON_ZERO' */;
+/*!40111 SET @OLD_SQL_NOTES=@@SQL_NOTES, SQL_NOTES=0 */;
+
+--
+-- Table structure for table `t_course`
+--
+
+DROP TABLE IF EXISTS `t_course`;
+/*!40101 SET @saved_cs_client     = @@character_set_client */;
+/*!40101 SET character_set_client = utf8 */;
+CREATE TABLE `t_course` (
+  `cid` int(11) DEFAULT NULL,
+  `name` varchar(50) DEFAULT NULL COMMENT '课程名',
+  `tid` int(11) DEFAULT NULL COMMENT '教师编号'
+) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4;
+/*!40101 SET character_set_client = @saved_cs_client */;
+
+--
+-- Dumping data for table `t_course`
+--
+
+LOCK TABLES `t_course` WRITE;
+/*!40000 ALTER TABLE `t_course` DISABLE KEYS */;
+/*!40000 ALTER TABLE `t_course` ENABLE KEYS */;
+UNLOCK TABLES;
+
+--
+-- Table structure for table `t_emp`
+--
+
+DROP TABLE IF EXISTS `t_emp`;
+/*!40101 SET @saved_cs_client     = @@character_set_client */;
+/*!40101 SET character_set_client = utf8 */;
+CREATE TABLE `t_emp` (
+  `emp_id` int(11) DEFAULT NULL,
+  `name` varchar(50) DEFAULT NULL,
+  `tel` char(11) DEFAULT NULL,
+  `salary` decimal(10,2) DEFAULT NULL,
+  `hire_date` date DEFAULT NULL
+) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4;
+/*!40101 SET character_set_client = @saved_cs_client */;
+
+--
+-- Dumping data for table `t_emp`
+--
+
+LOCK TABLES `t_emp` WRITE;
+/*!40000 ALTER TABLE `t_emp` DISABLE KEYS */;
+INSERT INTO `t_emp` VALUES (1,'jack','17189792205',13000.00,'2021-10-12'),(2,'lucy','17178982206',3200.00,'2022-11-15'),(3,'disen','17178979385',23000.00,'2022-10-12');
+/*!40000 ALTER TABLE `t_emp` ENABLE KEYS */;
+UNLOCK TABLES;
+
+--
+-- Table structure for table `t_score`
+--
+
+DROP TABLE IF EXISTS `t_score`;
+/*!40101 SET @saved_cs_client     = @@character_set_client */;
+/*!40101 SET character_set_client = utf8 */;
+CREATE TABLE `t_score` (
+  `sid` int(11) DEFAULT NULL,
+  `cid` int(11) DEFAULT NULL,
+  `score` decimal(5,2) DEFAULT NULL
+) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4;
+/*!40101 SET character_set_client = @saved_cs_client */;
+
+--
+-- Dumping data for table `t_score`
+--
+
+LOCK TABLES `t_score` WRITE;
+/*!40000 ALTER TABLE `t_score` DISABLE KEYS */;
+/*!40000 ALTER TABLE `t_score` ENABLE KEYS */;
+UNLOCK TABLES;
+
+--
+-- Table structure for table `t_stu`
+--
+
+DROP TABLE IF EXISTS `t_stu`;
+/*!40101 SET @saved_cs_client     = @@character_set_client */;
+/*!40101 SET character_set_client = utf8 */;
+CREATE TABLE `t_stu` (
+  `sid` int(11) DEFAULT NULL,
+  `name` varchar(20) DEFAULT NULL,
+  `sex` varchar(2) DEFAULT NULL,
+  `birthday` date DEFAULT NULL
+) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4;
+/*!40101 SET character_set_client = @saved_cs_client */;
+
+--
+-- Dumping data for table `t_stu`
+--
+
+LOCK TABLES `t_stu` WRITE;
+/*!40000 ALTER TABLE `t_stu` DISABLE KEYS */;
+INSERT INTO `t_stu` VALUES (1,'张三','女','1990-12-28'),(2,'王龙','男','1991-01-07'),(3,'刘冬冬','女','1992-08-21'),(4,'刘红','男','1998-02-15'),(5,'王玉玉','女',NULL);
+/*!40000 ALTER TABLE `t_stu` ENABLE KEYS */;
+UNLOCK TABLES;
+
+--
+-- Table structure for table `t_stu3`
+--
+
+DROP TABLE IF EXISTS `t_stu3`;
+/*!40101 SET @saved_cs_client     = @@character_set_client */;
+/*!40101 SET character_set_client = utf8 */;
+CREATE TABLE `t_stu3` (
+  `sid` int(11) DEFAULT NULL,
+  `name` varchar(20) DEFAULT NULL,
+  `sex` varchar(2) DEFAULT NULL,
+  `birthday` date DEFAULT NULL
+) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4;
+/*!40101 SET character_set_client = @saved_cs_client */;
+
+--
+-- Dumping data for table `t_stu3`
+--
+
+LOCK TABLES `t_stu3` WRITE;
+/*!40000 ALTER TABLE `t_stu3` DISABLE KEYS */;
+INSERT INTO `t_stu3` VALUES (1,'张三','女','1990-12-28'),(3,'刘冬冬','女','1992-08-21'),(5,'王玉玉','女',NULL);
+/*!40000 ALTER TABLE `t_stu3` ENABLE KEYS */;
+UNLOCK TABLES;
+
+--
+-- Table structure for table `t_tch`
+--
+
+DROP TABLE IF EXISTS `t_tch`;
+/*!40101 SET @saved_cs_client     = @@character_set_client */;
+/*!40101 SET character_set_client = utf8 */;
+CREATE TABLE `t_tch` (
+  `tid` int(11) DEFAULT NULL,
+  `name` varchar(50) DEFAULT NULL
+) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4;
+/*!40101 SET character_set_client = @saved_cs_client */;
+
+--
+-- Dumping data for table `t_tch`
+--
+
+LOCK TABLES `t_tch` WRITE;
+/*!40000 ALTER TABLE `t_tch` DISABLE KEYS */;
+/*!40000 ALTER TABLE `t_tch` ENABLE KEYS */;
+UNLOCK TABLES;
+/*!40103 SET TIME_ZONE=@OLD_TIME_ZONE */;
+
+/*!40101 SET SQL_MODE=@OLD_SQL_MODE */;
+/*!40014 SET FOREIGN_KEY_CHECKS=@OLD_FOREIGN_KEY_CHECKS */;
+/*!40014 SET UNIQUE_CHECKS=@OLD_UNIQUE_CHECKS */;
+/*!40101 SET CHARACTER_SET_CLIENT=@OLD_CHARACTER_SET_CLIENT */;
+/*!40101 SET CHARACTER_SET_RESULTS=@OLD_CHARACTER_SET_RESULTS */;
+/*!40101 SET COLLATION_CONNECTION=@OLD_COLLATION_CONNECTION */;
+/*!40111 SET SQL_NOTES=@OLD_SQL_NOTES */;
+
+-- Dump completed on 2023-08-24 17:01:50
diff --git a/day9/create_course.sql b/day9/create_course.sql
new file mode 100644
index 0000000..062c453
--- /dev/null
+++ b/day9/create_course.sql
@@ -0,0 +1,6 @@
+-- comment 表示字段的说明 (备份)
+create table t_course(
+    cid int,
+    name varchar(50) comment '课程名',
+    tid int comment '教师编号'
+);
diff --git a/day9/create_employee.sql b/day9/create_employee.sql
new file mode 100644
index 0000000..63f92cb
--- /dev/null
+++ b/day9/create_employee.sql
@@ -0,0 +1,10 @@
+use studb;
+
+-- 员工表
+create table t_emp(
+    emp_id int,
+    name varchar(50),
+    tel char(11),
+    salary decimal(10,2),
+    hire_date date
+);
diff --git a/day9/create_score.sql b/day9/create_score.sql
new file mode 100644
index 0000000..ee6a32a
--- /dev/null
+++ b/day9/create_score.sql
@@ -0,0 +1,5 @@
+create table t_score(
+    sid int,
+    cid int,
+    score decimal(5,2)
+);
diff --git a/day9/create_stu.sql b/day9/create_stu.sql
new file mode 100644
index 0000000..1f89058
--- /dev/null
+++ b/day9/create_stu.sql
@@ -0,0 +1,7 @@
+-- sql comment
+create table t_student(
+    sid int,
+    name varchar(20),
+    sex varchar(2),
+    birthday date
+);
diff --git a/day9/create_teacher.sql b/day9/create_teacher.sql
new file mode 100644
index 0000000..dadbe88
--- /dev/null
+++ b/day9/create_teacher.sql
@@ -0,0 +1,4 @@
+create table t_teacher(
+    tid integer,
+    name varchar(50)
+);
diff --git a/day9/delete_employee.sql b/day9/delete_employee.sql
new file mode 100644
index 0000000..594957e
--- /dev/null
+++ b/day9/delete_employee.sql
@@ -0,0 +1,4 @@
+use studb;
+
+delete from t_emp where hire_date > '2022-12-31';
+select * from t_emp;
diff --git a/day9/delete_students.sql b/day9/delete_students.sql
new file mode 100644
index 0000000..14b23f8
--- /dev/null
+++ b/day9/delete_students.sql
@@ -0,0 +1,8 @@
+-- 删除测试
+use studb;
+
+create table if not exists t_stu3
+select * from t_stu;
+
+delete from t_stu3
+where sex='男';
diff --git a/day9/insert_employee.sql b/day9/insert_employee.sql
new file mode 100644
index 0000000..a6305f6
--- /dev/null
+++ b/day9/insert_employee.sql
@@ -0,0 +1,10 @@
+use studb;
+
+insert into t_emp values
+(1,'jack','17189792205',12000,'2021-10-12'),
+(2,'lucy','17178982206',2200,'2022-11-15'),
+(3,'disen','17178979385',22000,'2022-10-12'),
+(4,'mack','17178982209',5000,'2023-08-15'),
+(5,'judy','17178982105',9000,'2023-08-20');
+
+select * from t_emp;
diff --git a/day9/insert_students.sql b/day9/insert_students.sql
new file mode 100644
index 0000000..3d5678f
--- /dev/null
+++ b/day9/insert_students.sql
@@ -0,0 +1,12 @@
+-- 单条数据插入
+insert into t_stu values(1,'张三','男','1991-01-15');
+
+-- 按照指定格式插入
+insert into t_stu(sid,name,birthday,sex)
+    values(2,'王龙','1990-12-18','男');
+
+-- 元组插入
+insert into t_stu values
+(3,'刘冬冬','女','1992-08-21'),
+(4,'刘红','女','1992-05-19'),
+(5,'王玉玉','女','1991-08-12');
diff --git a/day9/search_employee.sql b/day9/search_employee.sql
new file mode 100644
index 0000000..f8dbfa4
--- /dev/null
+++ b/day9/search_employee.sql
@@ -0,0 +1,3 @@
+use studb;
+
+select * from t_emp where salary>5000;
diff --git a/day9/search_students.sql b/day9/search_students.sql
new file mode 100644
index 0000000..810053e
--- /dev/null
+++ b/day9/search_students.sql
@@ -0,0 +1,5 @@
+-- 查询测试
+-- select * from t_stu where name like '刘';
+select * from t_stu where name like '刘%';
+
+select * from t_stu where birthday like '1991%';
diff --git a/day9/update_employee.sql b/day9/update_employee.sql
new file mode 100644
index 0000000..2eb4332
--- /dev/null
+++ b/day9/update_employee.sql
@@ -0,0 +1,10 @@
+use studb;
+
+update t_emp
+set salary = salary + 1000;
+
+update t_emp
+set salary = salary * 1.15
+where tel like '%8979$';
+
+select * from t_emp;
diff --git a/day9/update_students.sql b/day9/update_students.sql
new file mode 100644
index 0000000..7d89eb3
--- /dev/null
+++ b/day9/update_students.sql
@@ -0,0 +1,20 @@
+-- 修改测试
+update t_stu
+set sex='男',birthday='1998-02-15'
+where name = '刘红';
+
+update t_stu
+set sex='女',birthday='1990-12-28'
+where sid = 1;
+
+update t_stu
+-- set birthday=CURDATE()
+set birthday=null
+where sid = 5;
+
+/*
+update t_stu
+-- 使用函数加 5 天
+set birthday = DATE_ADD(birthday,INTERVAL 5 DAY)
+where sid = 2;
+*/